26 Miocene pinnipeds

Acrophoca longirostris, sometimes called the swan-necked seal, is an extinct genus of Late Miocene pinniped. It was thought to have been the ancestor of the modern leopard seal, however it is now thought to be a species of monk seal.

Aivukus is an extinct genus of walrus from the Miocene.

Allodesmus is an extinct genus of pinniped from the middle to late Miocene of California and Japan that belongs to the extinct pinniped family Desmatophocidae.

Archaeodobenus is an extinct genus of pinniped that lived during the Late Miocene of what is now Japan. It belonged to the Odobenidae family, which is today only represented by the walrus, but was much more diverse in the past, containing at least 16 genera. Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion.

Desmatophoca is an extinct genus of early pinniped that lived during the Miocene, and is named from the Greek "phoca", meaning seal. A taxon of the family Desmatophocidae, it shares some morphological similarities with modern true seals. Two species are recognized: Desmatophoca oregonensis and Desmatophoca brachycephala. Little information exists regarding Desmatophoca, due to the small number of fossil samples obtained and identified.

Enaliarctos is an extinct genus of pinniped, and may represent the ancestor to all pinnipeds. Prior to the discovery of Puijila, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene and early Miocene strata of California and Oregon.

Gomphotaria pugnax was a species of very large shellfish-eating dusignathine walrus found along the coast of what is now California, during the late Miocene. It had four tusks, with one pair in the lower and upper jaws, and according to wear on the tusks, G. pugnax hammered shellfish open, rather than simply sucking them out of their shells as do modern walruses. In terms of the postcranial skeleton, Gomphotaria and other dusignathine walruses were built more like sea lions than modern walrus. Gomphotaria is a prime example of the extreme diversity that walruses once exhibited.

Imagotaria is an extinct monotypic genus of walrus with the sole species Imagotaria downsi. Fossils of Imagotaria are known from the early late Miocene of California.

Ontocetus is an extinct genus of walrus, an aquatic carnivoran of the family Odobenidae, endemic to coastal regions of the southern North Sea and the southeastern coastal regions of the U.S. during the Miocene-Pleistocene. It lived from 13.6 mya—300,000 years ago, existing for approximately 13.3 million years .

Piscophoca is an extinct genus of pinniped. The genus was named after the fossiliferous Pisco Formation in Peru, where the holotype was found. Other fossils of the genus were found in the Bahía Inglesa Formation of the Caldera Basin in Chile.

Pliopedia pacifica is an extinct species of walrus found in what is now Central Valley, California, United States, which lived during the late Miocene. It was an amphibious carnivore.

Pontolis is a large extinct species of walrus. It contained only the single species Pontolis magnus.

Puijila darwini is an extinct species of basal pinniped which lived during the Miocene epoch about 21 to 24 million years ago. Approximately a metre in length, the animal possessed only minimal physical adaptations for swimming. Unlike modern pinnipeds, it did not have flippers and its overall form was otter-like, albeit more specialized; its skull and teeth are the features that most clearly indicate that it is a seal.

Semantoridae is an extinct family of stem-pinnipeds with fossils found in France, Kazakhstan, and Canada, dating back to various points in time in the Miocene epoch. Based on their overall anatomy semantorids were not marine specialists, as their elongated bodies, a long tail and robust limbs suggest they were freshwater animals not unlike otters. Indeed, at least some taxa such as Semantor and Potamotherium were initially classified as mustelids closely related to otters.

Thalassoleon is an extinct genus of large fur seal. Thalassoleon inhabited the Northern Pacific Ocean in latest Miocene and early Pliocene. Fossils of T. mexicanus are known from Baja California and southern California. T. macnallyae is known from central California, and T. inouei is known from Japan. Thalassoleon could be the ancestor of the modern northern fur seal.